1. Field of the Invention
The present invention relates to a multilayer resonator and a multilayer filter, each including a resonant circuit in a multilayer body defined by a laminate including a plurality of dielectric layers.
2. Description of the Related Art
A multilayer filter having a plurality of LC resonant circuits in a multilayer body defined by a laminate including a plurality of dielectric layers is used as a high-frequency filter. The LC resonant circuit may include a capacitor defined by opposed internal electrodes and an inductor defined by a via (for example, see Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2000-165171).
FIGS. 1A and 1B illustrate a known multilayer filter. FIG. 1A is a perspective view of the filter and FIG. 1B is a sectional view of the filter.
A laminate including five layers of insulating sheets 162A-162E is arranged as the multilayer filter 161. Vias 163A-163C are arranged in the insulating sheet 162A. Vias 164A-164C are arranged in the insulating sheet 162B. Vias 165A-165C, and coupling capacitors 166A and 166B are arranged in the insulating sheet 162C. Capacitor electrodes 167A-167C are arranged in the insulating sheet 162D. A capacitor electrode 168 is arranged on the insulating sheet 162E. A ground electrode 169C extending from the front surface (not shown) of the multilayer filter 161 to the rear surface (not shown) of the multilayer filter 161 via the top surface is also provided. An input-output terminal 169A is arranged on the left end surface of the multilayer filter 161 and an input-output terminal 169B is arranged on the right end surface of the multilayer filter 161.
In the multilayer filter 161, capacitor electrodes 167A and 167C are connected to the input-output terminals 169A and 169B and define resonant circuits at input-output stages. With this arrangement, routing lines for connecting the capacitor electrodes 167A and 167C to the input-output terminals 169A and 169B are required. The routing lines function as open stubs, and provide a parasitic inductive component to the LC resonator. For this reason, the multilayer filter 161 has an unwanted spurious component in frequency characteristics thereof, and has degraded attenuation characteristics.
When the ground electrode 169C is formed on the outer surface of the multilayer filter 161 by plating or other suitable method, loss in the vias 163A-163C increases due to corrosion of the vias 163A-163C. There is a risk that the frequency characteristics of the multilayer filter 161 will be degraded. During use, the vias 163A-163C are influenced by an external magnetic field of the multilayer filter 161. There is also a risk that the frequency characteristics of the multilayer filter 161 will be degraded.